The invention relates to a cardiac pacemaker of the type having a circuitry arrangement for varying at least one pacing parameter, in particular the pacing rate, as a function of a signal picked up in the patient's body as an input variable and correlated with physical exertion.
From European Patent A-0 140 472, a physiologically controlled cardiac pacemaker is known in which a pacing parameter, namely the basic pacing rate, is affected by the detected stroke volume or by a variable characteristic of the stroke volume.
The disadvantage here is that only the relative change in the variable characterizing the stroke volume is utilized for changing the heart rate, and there is no monitoring whatever as to whether the stroke volume does adequately follow up with the change in exertion, and only the necessary adaptation of the cardiac output to the physical exertion is assured. If the rate follows only the relative change in the stroke volume, then in rate ranges in which no stroke volume adaptation takes place, no adaptation of the rate is possible either--and consequently an absolute limit of physiological rate control is set, which comes particularly abruptly into play because with the reduced stroke volume adaptation capability, any rate adaptation is terminated as well.